In a papermaking machine it is necessary that the rolls be in axial alignment. For example, in the press section of the papermaking machine, the paper web is supported on a felt and passes between press rolls which serve to extract water from the paper web. If the rolls carrying the felt are not in precise axial alignment, the felt will tend to fold over, forming machine direction folds or creases in the felt. If the folds pass through the nip between the heavily loaded press rolls, the felt will be crushed and the paper web will be creased. Similarly, if the rolls in the forming section and dryer section of the papermaking machine are not aligned, the fabric will tend to wrinkle or fold with the result that the paper web will be correspondingly wrinkled or deformed.
In the past, various methods have been employed to maintain alignment of the rolls in the papermaking machine and one method of alignment has been to drop a plumb line at each end of the pair of rolls and any misalignment of the rolls can be visually ascertained.
However, the plumb line method is relatively inaccurate and does not provide a positive numerical indication of the degree of misalignment. Furthermore, after adjustment of a roll, it is necessary to re-check the alignment and again readjust the roll if necessary. Thus, the procedure is, in effect, a trial and error system.
The alignment of the rolls has also been determined by measuring the distance from the rolls to an outside object, such as the frame of the machine, which is known to be plumb. Again, this method of determining roll alignment is relatively inaccurate and does not provide a positive numerical value of the degree of misalignment. As in the case of the plumb line method, this method is a trial and error system.
The alignment of rolls has also been determined optically by use of a transit. This method provides a precise indication of roll alignment but requires specially skilled operators which are ordinarily not available in the papermaking plant.